FIG. 2 presents a conventional method for controlling a solenoid valve as is known from WO 2006/037715 A1. In this conventional method, a setpoint current value Is is compared in a comparator 28 with a measured current value Im, and the differential current value Id generated therefrom is fed to a current regulator (e.g. PID regulator) 14 which generates an actuating current value Ip therefrom. A ripple current value (dither signal) Ir which is made available by a modulation signal generator (e.g. dither unit) 18 is superimposed on the actuating current value Ip before a control signal generator (e.g. PWM unit) 20 generates therefrom a control signal S for controlling the solenoid valve 12. Here, the comparator 28 and the current regulator 14 are included in a master computer 10a which is already present in a control unit, for example, of a vehicle, while the dither unit 18 and the PWM unit 16 are included in an independent computer unit 10b. In addition, a filter means 22 is provided for the measured current value Im.
The object of the disclosed embodiments is to provide an improved method and an improved device for controlling a solenoid valve, by means of which method and device an armature of the solenoid valve can assume an intermediate position between an opened position and a closed position and can oscillate about this intermediate position with small deflections, and which permit a simple design and a minor need for computing power.
This object is achieved by the teaching of the independent claims. Advantageous configurations of the invention are the subject-matter of the dependent claims.
The method according to the invention for controlling a solenoid valve comprises the following steps:                generating a setpoint current value on the basis of a target current value, wherein a ripple current value is superimposed on the target current value;        comparing the setpoint current value with a measured current value and generating a differential current value;        generating an actuating current value from the differential current value in a current regulator; and        generating a control signal for controlling the solenoid valve from the actuating current value in a control signal generator.        
In contrast to the conventional method described at the beginning, the invention proposes already integrating a ripple current value into the setpoint current value in order to generate oscillations of the armature of the solenoid valve about its centre position. As a result, the entire method for controlling the solenoid valve can be carried out in just one computer unit or just one device. The total computing power required can also be reduced compared for example to the conventional method illustrated in FIG. 2.
In an advantageous configuration of the invention, the ripple current value is formed from a setpoint value of amplitude of ripple current and a setpoint value of frequency of ripple current. In other words, the amplitude and the frequency of the ripple current value can be adjusted.
In another advantageous configuration of the invention, a time profile of the ripple current value forms a triangular signal. Such a triangular signal is relatively easy to calculate, with the result that overall less computing power is required. Therefore, for example fewer reference points are necessary for the calculation of a triangular signal than for a sine signal.
In another advantageous configuration of the invention, the setpoint current value is generated by means of software technology.
In yet another advantageous configuration of the invention, an ampflication signal, which is preferably generated from a comparison of the setpoint current value with the measured current value, is superimposed on the actuating current value generated by the current regulator.
The device according to the invention for controlling a solenoid valve comprises a comparator to which a setpoint current value and a measured current value are fed and which generates a differential current value; a current regulator to which the differential current value is fed and which generates an actuating current value; and a control signal generator to which the actuating current value is fed and which generates a control signal for controlling the solenoid valve. According to the invention, the device additionally has a setpoint current value generator which is configured to generate the setpoint current value on the basis of a target current value and a ripple current value.
The same advantages can be achieved with this device as with the method of the invention as described above.
In an advantageous configuration of the invention, the setpoint current value generator is configured to generate the setpoint current value on the basis of the target current value, a setpoint value of amplitude of ripple current and a setpoint value of frequency of ripple current.
In an advantageous configuration of the invention, a time profile of the ripple current value forms a triangular signal.
In another advantageous configuration of the invention, the setpoint current value generator is configured as a software solution.
In yet another advantageous configuration of the invention, an amplifier means is additionally provided which superimposes an amplification signal, which is preferably generated from a comparison of the setpoint current value with the measured current value, on the controlling current value generated by the current regulator.